Figure 4. The folding status of an antibody domain controls IgG secretion in vivo.

(A) COS-1 cells were co-transfected with vectors encoding BiP and either a wild type light chain (LC_wt), a light chain containing the C_H1 domain instead of the C_L domain (LC_CH1), or a light chain containing an unfolded C_L domain (LC_CLmut). Cells were metabolically labeled for 3 h and both cell lysates (no subscript) and culture supernatants (subscript m) were immunoprecipitated with the indicated antisera (Ab). Precipitated proteins were separated by SDS-PAGE under reducing conditions and visualized by autoradiography. (B) COS-1 cells were co-transfected as in (A) except that a vector encoding a chimeric humanized mouse heavy chain was also included. Cells were labeled and analyzed as in (A). (C) COS-1 cells were co-transfected with vectors encoding BiP, a Flag-tagged truncated heavy chain consisting of only the V_H and C_H1 domains (Lee et al., 1999), and with the indicated light chain constructs (i.e., λ, wild type κ, or C_L mutant κ). Cells were metabolically labeled and both cell lysates (L) and culture supernatants (M) were immunoprecipitated with the anti-Flag antibody. Precipitated proteins were separated by SDS-PAGE under non-reducing condition (except the first lane, which included 2-ME in the sample buffer and is indicated as red) and visualized by autoradiography. Mobilities of completely reduced (ox₀), partially oxidized (ox₁), and fully oxidized (ox₂) forms of truncated heavy chain, as well as those of λ and κ light chains are indicated. The tagged forms of the κ light chain constructs co-migrate with the ox1 form of the truncated heavy chain.